The present invention relates to an improved pump for compression of gases, such as air, comprising a first, stationary cylinder, wherein a piston is arranged for movement in the longitudinal direction of said cylinder so as to divide the latter into a first chamber located ahead of the piston, and a second chamber located behind the piston, a piston rod securely joining said piston to a second movable cylinder arranged externally of the first cylinder so as to ensure co-ordination of the movements of said piston and said second cylinder. The open end of said second cylinder is sealed against the external face of the first cylinder and the open end of the first cylinder is sealed against the internal wall of the second cylinder, whereby a third chamber is formed between the seals.
Pumps of the above kind are known from SE 463 732 and could be regarded as a two-step pump because the compression of air takes place in two steps, viz. both when the cylinders pushed together and when the are pulled apart. Owing to this double compression feature, this type of pump is quite superior to the conventional bicycle pump when it comes to producing comparatively high pressures by means of comparatively moderate forces. However, when sufficiently high pressures are required, for example in the magnitude of 200 bars, pumps of the kind defined above are not satisfactory either. Pressures of this magnitude are required for instance for high-pressure cartridges for air guns.
The object of the present invention is to provide a pump of the kind defined in the introduction, which offers an improved degree of compression by means of substantially unchanged forces.
The compression of air thus is effected in three steps. The first step takes place, when the air in the fourth chamber is forced into the second and third chambers. Since the goods in the first cylinder occupies some of the space between the second and third chambers, the total cross-sectional area of these chambers is inferior to the cross-sectional area of the fourth chamber, and consequently compression of the air takes place.
The second step is effected when the air is forced from the second and third chambers into the first chamber. The latter chamber has a considerable smaller cross-sectional area than the first-mentioned ones, since it is limited by the first, smallest cylinder. Consequently, the Air is Compressed Further in this Step.
The third step takes places exactly like in the above two-step pump, when the air in the second chamber is forced out through the outlet formed in the first end of the first cylinder.
The through-passage valve in the second cylinder inlet could be made adjustable to allow adjustment of the flow through the inlet. By throttling the inflow, the pumping movements consume less power because less air is introduced into the pump and consequently less compression work is done. If said through-passage valve is throttled, a predetermined negative pressure is created in the fourth chamber when the pumping house is extended in the course of the upwardly directed pumping movement.
Obviously, other gases than air could be compressed by means of the pump in accordance with the invention.
In accordance with a preferred embodiment a third cylinder, which is fixedly interconnected with the first cylinder surrounds the second cylinder. This third cylinder has sealing contact with the end wall of the second cylinder, whereby a fifth chamber is formed between said end wall and one end of the third cylinder. This fifth chamber communicates with said third chamber via a first through-passage valve and with the environment via a second through-passage valve.
In this case, when the second cylinder and the piston rod are moved away from the first cylinder, the pump is arranged to draw air past said second through-passage valve into the fifth chamber and in doing so close said first through-passage valve, and to force air from the fifth chamber past said first through-passage valve into the third chamber, and in doing so close said second through-passage valve.
In accordance with this embodiment, a three-step pump with double compression in the first step is provided. As described above, air passing from the fourth chamber to the second and third chambers is compressed, as is also air passing from the fifth chamber to said second and third chambers.
Since the two compression operations take place simultaneously, a considerable improvement of the total compression is achieved.